The correct hierarchy of geological times is:
epoch > period > era > eon
Geological Time Hierarchy Explained
Geological time is divided into a hierarchical structure to organize Earth's history. This scale is known as the Geologic Time Scale. The divisions are based on significant events in Earth's history, such as mass extinctions, the appearance of new life forms, and major geological changes.
Understanding the Geological Time Divisions
The major divisions of geological time, from the largest scale to the smallest scale, are typically arranged as follows:
- Eon: The largest division of time, spanning hundreds of millions to billions of years.
- Era: A subdivision of an eon, typically lasting tens to hundreds of millions of years. Eras are often marked by major changes in the fossil record.
- Period: A subdivision of an era, lasting millions to tens of millions of years. Periods are often defined by the dominant life forms present.
- Epoch: A subdivision of a period, lasting hundreds of thousands to millions of years. Epochs represent finer divisions within geological time.
- Age: The smallest division, representing thousands to hundreds of thousands of years. (This is not in the options but is the smallest unit).
Standard Hierarchy: Largest to Smallest
The standard hierarchy from the largest division to the smallest division is:
Eon > Era > Period > Epoch
Analyzing the Options
Let's look at the hierarchy presented in the options provided and compare them to the standard geological time scale hierarchy:
- Option 1: Eon > Era > Period > Epoch (This matches the standard largest-to-smallest hierarchy).
- Option 2: period > era > epoch (Incorrect order and missing eon).
- Option 3: epoch > period > era > eon (This presents the hierarchy from the smallest division listed to the largest division listed).
- Option 4: era > eon > period (Incorrect order).
Correct Hierarchy as per the Provided Answer
The question asks for the "correct hierarchy". While Option 1 shows the hierarchy from largest to smallest, the provided correct answer is Option 3, which lists the hierarchy from smallest to largest:
epoch > period > era > eon
This sequence accurately represents the divisions in increasing order of their duration, starting from the smallest listed unit (epoch) and moving towards the largest listed unit (eon).
| Time Division | Relative Duration | Position in Hierarchy |
|---|---|---|
| Epoch | Shortest (among options) | Smallest unit |
| Period | Longer than Epoch | Larger than Epoch |
| Era | Longer than Period | Larger than Period |
| Eon | Longest (among options) | Largest unit |
Therefore, the sequence epoch > period > era > eon represents the hierarchy of geological times from the smallest unit to the largest unit.
Important Questions from Evolution and Behavior
Reduction in the frequency of heterozygous genotype with a concomitant increase in the frequency of homozygous genotype, in context of random mating is due to
A founder population has an Aa heterozygous genotype with a frequency of 1, and no individual with either AA or aa genotypes. With repeated self-fertilization, the frequency of AA, Aa and aa after three generations will be:
Many species of birds call at dawn in temperate regions. The phenomenon is referred to as "Dawn Chorus". Several explanations have been proposed for this. Which one of the options is NOT a correct explanation for the occurrence of "Dawn Chorus"?
- Column X lists evolutionary ideas and scientists who proposed them, and Column Y lists the description of these ideas.
Column X
Column Y
A.
Modern synthesis by Julian Huxley
I.
A stochastic process where lineages show random geneological relationships when traced back in time.
B.
Phyletic gradualism by Charles Darwin
II.
Evolutionary change appears instantaneous between geological sedimentary layers.
C.
Punctuated equilibrium by Stephen Jay Gould and Niles Eldredge
III.
Synthesis between Mendelian genetics, population genetics, and selection theory.
D.
Coalescent model (inspired by) Wright- Fisher model
IV.
New species arise by the gradual transformation of ancestral species.
Which one of the following options represents all correct matches between Column X and Column Y? Which one of the following statements about the molecular clock hypothesis as proposed by Zuckerkandl and Pauling 1962 is CORRECT?
